1. Technical Field
This invention relates to sheet-fed machines and in particular sheet-fed machines printing on both sides of the fed sheets and having laterally adjustable sheet guides.
2. Description of the Related Art
In a sheet-fed machine, the sheets are held and guided in their path by various sheet guides so that the sheets may be reliably conveyed through the machine without flapping.
When the sheet guide means need to be adjusted to a different position by the machine operator for one reason or another, the sheet-fed machine has to be switched off. The sheet guides in the machine are practically never accessible to the operating staff, so that at least two workers have to cooperate on call in order to be able to adjust the sheet guides. In the usual case the guides are adjusted in accordance with the printed text conditions at any given time, in order that the guides contact the sheets only at non-printing areas to avoid smearing of the sheets. After alignment, a test run has to be carried out to check the effect of the adjustment. Depending on the result, further re-adjustment with the machine switched off may have to be carried out. An appreciable loss of time during printing and an additional responsibility for the operating staff therefore result.
West German Patent (DE-AS) No. 1,561,101 published Jan. 8, 1970 discloses a sheet guide system for sheet guide cylinders in multi-colour sheet-fed rotary printing machines. To avoid smearing of the freshly printed surface this system comprises, beneath the printing cylinder and the sheet guide cylinder, a number of hollow sheet guide stirrups with air exit apertures. The sheet guide means in the form of retaining discs are axially displaceable on the sheet guide cylinder. The sheet guide means can thus be disposed at those places where there is no ink applied to the sheet. The object of this system is correct-register guidance of the sheet end when the front edge of the sheet has already been released, allowing for the format adjustment in the case of continuous printing and intermittent operation.
Another problem in the setting-up and adjustment of the sheet guides in more recent machines is that the sheet guides are covered by plates and hoods so that they can no longer be seen directly from outside, i.e. accessibility of the sheet guide means in the recent machines is very much poorer than in the older machines.
As a result of these deficiencies, operating staff are usually compelled to go into or beneath the sheet-fed machine in order to carry out the adjustment operation. Corrections are usually necessary in succession for the above-mentioned reasons of difficulty, resulting in considerable down-time or loss of time for continuous printing.
In the case of sheet guide wheels, it was, for example, a complex procedure first to release a retaining pin and then shift the wheels on their mounting shaft. The retaining pin then had to be relocked to enable the sheet guide rollers to be rigidly secured in the required position on the shaft in order to avoid print smearing.
This procedure of adjustment and alignment with the machine stationary was very time-consuming and difficult to perform.